1. Field of the Invention
The present invention relates to an actuator for use in automotive safety equipment and more particularly to, for example, an actuator for use in an operation such as one for raising a hood panel of an automobile when receiving a pedestrian as an object to be protected by the hood panel.
2. Related Art
Conventionally, as actuators for safety equipment mounted on motor vehicles, there have been actuators for raising a rear end side of a hood panel so as to receive a pedestrian by the hood panel itself by making use of energy absorption taking place when the hood panel is plastically deformed (for example, refer to JP-A-2004-330912).
The actuators were configured as actuators of a piston cylinder type in which gas generated when a gas generator was activated was used as a drive source, so as to be put into operation quickly. In the actuators so configured, gas generated as working fluid when the gas generator was activated was filled within the cylinder so as to raise the piston rod housed in the cylinder, so that the hood panel supported on an upper end side of the piston rod could be raised. In addition, the piston rod was constructed into something like one in which the piston was integrated with a support rod which extended from the piston so as to support the hood panel. Further, in the actuator, a lock mechanism was built therein so as to restrict a descending movement of the piston rod that had once been raised relative to the cylinder so as to prevent the descending movement of the hood panel after the hood panel had once been raised by gas from the gas generator being filled within the cylinder.
This lock mechanism was constructed in such a manner that a C ring which was made of a wire material having a circular cross section and was made to be elastically deformed in a diametrical contracting direction was disposed in an accommodating groove provided on an inner circumferential surface side of the cylinder in a circumferential direction, that an outer circumferential surface side of the piston rod was made to slide on an inner circumferential surface of the cylinder along a substantially full length of the cylinder and that a fitting groove into which the C ring was allowed to fit was disposed on the outer circumferential surface of the piston rod in a position where locking was desired to take place. In this lock mechanism, when the actuator was activated, the piston rod was caused to ascend, and the portion of the piston rod where the locking groove was provided was disposed in the portion of the cylinder where the accommodating groove was provided, whereby the C ring was diametrically contracted so as to enter the fitting groove in such a way as to extend between the accommodating groove on the inner circumferential side of the cylinder and the fitting groove on the piston rod, a descending movement of the piston rod being thereby restricted.
In the conventional actuators, however, the accommodating groove side surface and the fitting groove side surface which confronted each other across the C ring when the lock mechanism was activated were both made into not surfaces which were directed in a direction which was at right angles to the axial direction of the piston rod but the taper surfaces which were parallel to each other in such a manner as to diametrically expand as they extended upwards. Because of this, in the event that the C ring behaved as being diametrically expanded in a radially outward direction of the cylinder between the confronting taper surfaces when locking took place, it became difficult to restrict the diametrical expansion of the C ring due to a lower surface side of the cylinder side accommodating groove being formed in such a manner as to be diametrically expanded in an upward direction, leading to a fear that the C ring was allowed to pop out from the interior of the fitting groove on the piston rod to thereby easily cancel the locked state. Thus, there was room for improvement.
In particular, in the event that the actuator is configured such that the piston rod which projects from the cylinder after the activation of the actuator is made to project from the cylinder and is made to be bent and plastically deformed so as to absorb the kinetic energy of an object to be protected when the receiving member receives the object to be protected, a compression stress is applied to the piston rod along the axial direction thereof, and this compression stress is combined with a bending stress along the direction which is at right angles to the axis of the piston rod so as to be applied to the piston rod. As this occurs, a minute sliding gap exists in the location of the piston rod which slides within the cylinder, and this gap is combined with an action of the piston rod in which the piston rod is inclined in the direction which is at right angles to the axis of the piston rod within the cylinder, whereby with no action taken to cope with this, there tends to be caused a fear that the C ring moves in the way described above when locking takes place, as a result of which the cancellation of the locked state is facilitated further.
Further, in a case where the outside diametrical dimension of the piston rod is changed so as to adjust the bending rigidity of the piston rod in order to adjust the absorption amount of kinetic energy of the object to be protected when the piston rod is bent and plastically deformed, in the conventional actuators, since the construction is adopted in which the outer circumferential surface of the piston rod is made to slide on the inner circumferential surface of the cylinder along the substantially full length of the piston rod with the C ring interposed therebetween, the change is not limited to a change in the piston rod, and the inside diameter of the cylinder also needs to be changed. Thus, the adjustment of kinetic energy absorption amount has not been easy to be dealt with.